Yes, I thought of that too. If you get a butane adapter like this:
You can connect it to the refiller you linked to:
and fill up to 70% with butane.
Then hook up a propane adapter like the one you pointed out:
and fill the remaining 30% with propane.
Dangerous as all get out if overdo it, but the capability is there. Safer I think to just transfer from one standard backpacking type canister to the other with pre-mixed blends.
Of course, for the very brave, you can "spike" your mix with extra propane. If you keep the canister cold, it should be OK, but you'd want to be EXTREMELY assiduous about keeping that canister cold. Forget and leave it in your pack when you come back to your nice warm home, and... Well, it might be bad anyway. Opens up a lot of possibilities and a lot of dangers at the same time.
Now, I can make my own winter blends though. Quite interesting.
Adventures in Stoving